Blood glucose is an important marker for diabetes. In the fermentative production using microorganisms, glucose levels are assayed for monitoring the process. Conventional glucose assays were based on enzymatic methods using a glucose oxidase (GOD) or glucose-6-phosphate dehydrogenase (G6PDH). However, GOD-based assays required addition of a catalase or peroxidase to the assay system in order to quantitate the hydrogen peroxide generated by glucose oxidation reaction. G6PDHs have been used for spectrophotometric glucose assays, in which case a coenzyme NAD(P) had to be added to the reaction system.
Accordingly, an object of the present invention is to provide a modified water-soluble PQQGDH with improved affinity for glucose. Another object of the present invention is to provide a modified water-soluble PQQGDH with high selectivity for glucose in order to increase the sensitivity for measuring blood glucose levels.